####
**Raw Data:**

Raw data are collected data that have not been organized in any way.

####
**Array:**

An array is a list of raw numerical data in ascending or descending order of magnitude.

####
**Frequency Distribution:**

When summarizing large no of data, we categorized them into classes or categories and no of individuals belongs to each class is called the

**Class Frequency**.

A tabular arrangement of data by classes or categories with class frequency is called

**Frequency Distribution**.

####
Example:

Below is the table for 100 students and their heights categories -

**Height (in)** |
**No of Students** |

60-62 |
5 |

63-65 |
18 |

66-68 |
38 |

69-71 |
31 |

72-74 |
8 |

**total** |
**100** |

####
**
Class Intervals and Class Limits:**

A symbol defining a class is called

**Class Intervals **such as 63-65, also called

**Closed Class Intervals **as Class has end numbers.

The end no of the class is called

**Class Limits **such as 66 and 68 where 66 is

**Lower Class Limit** and 68 is

**Upper-Class Limit. ** If Class has either no upper class nor no lower class is called an

**Open Class Intervals **such as category 65+years.

####
**
Class Boundaries:**

Class Boundaries can be defined by adding upper-class limit if a category to lower class limit of the next category by 2.

Upper-Class Boundary (n) - { UCL(n) + LCL(n+1) } / 2

For

63-65 category, 65.5 { (65+66)/2 } is upper-class limit and 62.5 { (62+63)/2 } is lower class limit.

####
**Size/Width of a Class Interval:**

The difference between the lower and upper-class limit is called size or width of a Class Interval.

such as -

For

63-65 category, Width is - 65.5 - 62.5 = 3
####
**The Class Mark:**

The Class Mark is mid-point of a Class interval and can be calculated as below -

Class Mark (n) - { UCL(n) + LCL(n) } / 2

For

63-65 category, Class Mark is - (63 + 65) / 2 = 64
Histogram and Frequency Polygon are two graphic representation of frequency distribution. We will discuss this more in the next post.

Till then, Happy Learning.........

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